U.S. patent application number 10/361917 was filed with the patent office on 2003-08-21 for charge/discharge control method for battery pack and charge/discharge control apparatus for battery pack.
Invention is credited to Ishishita, Teruo.
Application Number | 20030155891 10/361917 |
Document ID | / |
Family ID | 27678403 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030155891 |
Kind Code |
A1 |
Ishishita, Teruo |
August 21, 2003 |
Charge/discharge control method for battery pack and
charge/discharge control apparatus for battery pack
Abstract
It is an object of the invention to provide a charge/discharge
control apparatus for a battery pack which is capable of performing
SOC control and reducing the SOC variation through simple
processes, and a control method thereof. In order to achieve the
aforementioned object, A charge/discharge control apparatus for a
battery pack having a plurality of cells according to one aspect of
the invention includes a voltage detection portion that measures a
voltage of each set of a predetermined number of cells provided in
the battery pack, a computation portion that computes a state
quantity of each set of the predetermined number of cells based on
the voltage measured by the voltage detection portion, and a
charge/discharge control portion that performs a charge/discharge
control based on a least state quantity that is a least one of the
state quantities of the sets of the predetermined number of
cells.
Inventors: |
Ishishita, Teruo;
(Nishikamo-gun, JP) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET, N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
27678403 |
Appl. No.: |
10/361917 |
Filed: |
February 11, 2003 |
Current U.S.
Class: |
320/134 |
Current CPC
Class: |
Y02E 60/10 20130101;
G01R 31/3835 20190101; H01M 6/42 20130101; G01R 31/396 20190101;
G01R 31/3648 20130101; H01M 10/44 20130101 |
Class at
Publication: |
320/134 |
International
Class: |
H02J 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2002 |
JP |
2002-043216 |
Claims
What is claimed is:
1. A charge/discharge control apparatus for a battery pack having a
plurality of cells, comprising: a voltage detection portion that
measures a voltage of each set of a predetermined number of cells
provided in the battery pack; a computation portion that computes a
state quantity of each set of the predetermined number of cells
based on the voltage measured by the voltage detection portion; and
a charge/discharge control portion that performs a charge/discharge
control based on a least state quantity that is a least one of the
state quantities of the sets of the predetermined number of
cells.
2. The charge/discharge control apparatus according to claim 1,
wherein each set of the predetermined number of cells is a single
cell, and wherein the voltage detection portion measures a voltage
of each single cell of the battery pack, and the computation
portion computes a state quantity of each single cell.
3. The charge/discharge control apparatus according to claim 1,
wherein each set of the predetermined number of cells has an
arrangement of a battery block in which a plurality of cells are
connected in series, and wherein the voltage detection portion
measures a voltage of each battery block, and the computation
portion computes a state quantity of each battery block.
4. The charge/discharge control apparatus according to claim 1,
wherein the state quantity is a remaining capacity value of each
set of the predetermined number of cells based on the voltage
measured.
5. The charge/discharge control apparatus according to claim 1,
wherein the state quantity is a percentage of a remaining capacity
value of each set of the predetermined number of cells based on the
voltage measured, with respect to a fully charged capacity
value.
6. The charge/discharge control apparatus according to claim 1,
further comprising an overcharge determining portion that performs
an overcharge determination as to whether an overcharged state
exists based on a greatest state quantity that is a greatest one of
the state quantities of the sets of the predetermined number of
cells.
7. The charge/discharge control apparatus according to claim 6,
wherein each set of the predetermined number of cells is a single
cell, and wherein the greatest state quantity is a greatest one of
the state quantities of the single cells.
8. The charge/discharge control apparatus according to claim 6,
wherein each set of the predetermined number of cells has an
arrangement of a battery block in which a plurality of cells are
connected in series, and wherein the greatest state quantity is a
greatest one of the state quantities of the battery blocks.
9. The charge/discharge control apparatus according to claim 6,
wherein the state quantity is a remaining capacity value of each
set of the predetermined number of cells based on the voltage
measured.
10. The charge/discharge control apparatus according to claim 6,
wherein the state quantity is a percentage of a remaining capacity
value of each set of the predetermined number of cells based on the
voltage measured, with respect to a fully charged capacity
value.
11. A charge/discharge control method for a battery pack having a
plurality of cells, comprising: measuring a voltage of each set of
a predetermined number of cells provided in the battery pack;
computing a state quantity of each set of the predetermined number
of cells based on the voltage measured; and performing a
charge/discharge control based on a least state quantity that is a
least one of the state quantities of the sets of the predetermined
number of cells.
12. The charge/discharge control method according to claim 11,
wherein each set of the predetermined number of cells is a single
cell, and a voltage of each single cell of the battery pack is
measured, and a state quantity of each single cell is computed.
13. The charge/discharge control method according to claim 11,
wherein each set of the predetermined number of cells has an
arrangement of a battery block in which a plurality of cells are
connected in series, and a voltage of each battery block is
measured, and a state quantity of each battery block is
computed.
14. The charge/discharge control method according to claim 11,
wherein the state quantity is a remaining capacity value of each
set of the predetermined number of cells based on the voltage
measured.
15. The charge/discharge control method according to claim 11,
wherein the state quantity is a percentage of a remaining capacity
value of each set of the predetermined number of cells based on the
voltage measured, with respect to a fully charged capacity
value.
16. The charge/discharge control method according to claim 11,
further comprising performing an overcharge determination as to
whether an overcharged state exists based on a greatest state
quantity that is a greatest one of the state quantities of the sets
of the predetermined number of cells.
17. The charge/discharge control method according to claim 16,
wherein each set of the predetermined number of cells is a single
cell, and wherein the greatest state quantity is a greatest one of
the state quantities of the single cells.
18. The charge/discharge control method according to claim 16,
wherein each set of the predetermined number of cells has an
arrangement of a battery block in which a plurality of cells are
connected in series, and wherein the greatest state quantity is a
greatest one of the state quantities of the battery blocks.
19. The charge/discharge control method according to claim 16,
wherein the state quantity is a remaining capacity value of each
set of the predetermined number of cells based on the voltage
measured.
20. The charge/discharge control method according to claim 16,
wherein the state quantity is a percentage of a remaining capacity
value of each set of the predetermined number of cells based on the
voltage measured, with respect to a fully charged capacity value.
Description
INCORPORATION BY REFERENCE
[0001] The disclosure of Japanese Patent Application No.
2002-043216 filed on Feb. 20, 2002 including the specification,
drawings and abstract is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a charge/discharge control
apparatus and method for a battery pack in which a plurality of
battery cells are connected in series, and to a control method
thereof.
[0004] 2. Description of the Related Art
[0005] Hybrid vehicles incorporating an electric power generator
driven by an engine, in addition to a vehicle-driving electric
motor, have been known. Such a hybrid vehicle has a battery pack in
which a plurality of battery cells are connected in series. Using
electric power from the battery pack, the vehicle-driving electric
motor is driven. Electric power from the generator is stored into
the battery pack.
[0006] FIG. 3 illustrates the construction of a charge/discharge
control apparatus for a battery pack as mentioned above. Referring
to FIG. 3, a battery pack 12 is formed by a plurality of battery
cells 10 connected in series. A voltage detector 14 for detecting
the voltage of the individual cells 10 is connected to the battery
pack 12. On the basis of an output of the voltage detector 14, a
battery ECU 16 computes the state of charge SOC of the cells
10.
[0007] Normally, the battery pack 12 has an arrangement in which a
plurality of battery blocks each formed by a plurality of battery
cells 10 connected in series are connected in series. Therefore,
the value of voltage detected by the voltage detector 14 may be the
value of voltage of each cell 10 as mentioned above, or may be the
value of voltage of each battery block. In the latter case, the
battery ECU 16 computes the state of charge SOC of each battery
block from the value of voltage of the battery block. On the basis
of the thus-computed SOC value, an HVECU 18 controls loads 20 that
include a vehicle-driving electric motor, a generator-driving
engine, a generator, an inverter, etc., and performs control of
adjusting the amount of charge of the battery pack 12 so that the
SOC value of the battery pack 12 is within a predetermined range. A
typically adopted control range of SOC is, for example, the range
of 20% to 80%. An SOC control method for the battery pack 12 as
described above is disclosed in Japanese Patent Application
Laid-Open Publication No. 2000-14029.
[0008] The foregoing related-art control apparatus performs control
such that the SOC of the battery pack 12 is within a predetermined
range (e.g., of 20% to 80%). In this case, a battery block that
exhibits the lower limit value (20%) of the control range is
different from a battery block that exhibits the upper limit value
(80%) of the control range. That is, if a control is performed such
that the SOC of the battery pack 12 will not fall below the lower
limit value of the control range, the control is performed as
follows. That is, the remaining capacity of each battery block is
determined from the voltage thereof. The SOC value of the battery
block that exhibits the least value of the thus-determined
remaining capacities is set as a least SOC value for use in the
control of the SOC of the battery pack 12. The control is performed
so as to prevent the least SOC value from falling below the lower
limit value. If a control is performed such that the SOC of the
battery pack 12 will not exceed the upper limit value of the
control range, the control is performed as follows. That is, the
SOC value of the battery block that exhibits the greatest value of
the remaining capacities of the battery blocks is set as a greatest
SOC value of the battery pack 12. The control is performed so as to
prevent the greatest SOC value from increasing above the upper
limit value.
[0009] The charge/discharge capabilities of the individual cells 10
vary with increasing time of use of the battery pack 12. That is,
the variation in SOC among the cells 10 or the battery blocks is
small as indicated in FIG. 4(2) during an initial period of use of
the battery pack 12. However, as time elapses, the variation in SOC
becomes greater as indicated in FIG. 4b.
SUMMARY OF THE INVENTION
[0010] In the case of the above-described related-art
charge/discharge control apparatus, however, it is necessary to
compute both the least value and the greatest value of SOC of the
cells 10 or the battery blocks. Moreover, it is necessary to
perform the control regarding the lower limit value of SOC through
the use of the least value and the control regarding the upper
limit value of SOC through the use of the greatest value separately
from each other. Therefore, the related-art apparatus has a problem
of complicated computation processes.
[0011] Furthermore, the variation in SOC among the cells 10 or
among the battery blocks becomes great as indicated in FIG. 4b.
Correspondingly, the SOC control precision decreases. Therefore, it
becomes necessary to perform a uniformalization control of reducing
the SOC variation among the battery cells by overcharging the cells
10 or the battery blocks. Due to the overcharging of the cells, the
uniformalization control gives rise to a problem of reduced service
life of the cells.
[0012] Accordingly, it is an object of the invention to provide a
charge/discharge control apparatus for a battery pack which is
capable of performing SOC control and reducing the SOC variation
through simple processes, and a control method thereof
[0013] In order to achieve the aforementioned object, a
charge/discharge control apparatus for a battery pack having a
plurality of cells according to one aspect of the invention
includes a voltage detection portion that measures a voltage of
each set of a predetermined number of cells provided in the battery
pack, a computation portion that computes a state quantity of each
set of the predetermined number of cells based on the voltage
measured by the voltage detection portion, and a charge/discharge
control portion that performs a charge/discharge control based on a
least state quantity that is a least one of the state quantities of
the sets of the predetermined number of cells.
[0014] According to the above-described construction, the
charge/discharge control of the battery pack is performed using
only the least one of the state quantities of the cells or the
battery blocks of the battery pack. Therefore, the computation of
SOC can be simplified. Furthermore, although execution of control
of the upper limit value of SOC through the use of the least state
quantity tends to further increase the amounts of charge of the
cell with the greatest capacity value and cells having capacity
values close to the greatest capacity value, actual SOC increases
are curbed due to increases in self-discharge and decreases in
charging efficiency. Therefore, the apparatus of the invention is
able to curb the SOC variation without performing the
uniformalization control by overcharging the cells.
[0015] In the above-described charge/discharge control apparatus
for the battery pack, each set of the predetermined number of cells
may be a single cell or a battery block in which a plurality of
cells are connected in series.
[0016] Furthermore, in the charge/discharge control apparatus, the
state quantity may be a remaining capacity value of each set of the
predetermined number of cells based on the voltage, or may be a
percentage of the remaining capacity value to a fully charged
capacity value.
[0017] Further, the charge/discharge control apparatus may further
include an overcharge determining portion that performs an
overcharge determination as to whether an overcharged state exists
based on a greatest state quantity that is a greatest one of the
state quantities of the sets of the predetermined number of
cells.
[0018] According to this construction, the overcharge determination
is performed on the basis of the greatest one of the state
quantities of the sets of the predetermined number of cells.
Therefore, it becomes possible to prevent the service life
reduction of the cells caused by the overcharging of the cells of
the battery pack.
[0019] In accordance with another aspect of the invention, a
charge/discharge control method for a battery pack having a
plurality of cells includes measuring a voltage of each set of a
predetermined number of cells provided in the battery pack,
computing a state quantity of each set of the predetermined number
of cells based on the voltage measured, and performing a
charge/discharge control based on a least state quantity that is a
least one of the state quantities of the sets of the predetermined
number of cells.
[0020] In the above-described charge/discharge control method for
the battery pack, each set of the predetermined number of cells may
be a single cell or a battery block in which a plurality of cells
are connected in series.
[0021] Furthermore, in the charge/discharge control method, the
state quantity may be a remaining capacity value of each set of the
predetermined number of cells based on the voltage, or may be a
percentage of the remaining capacity value to a fully charged
capacity value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The foregoing and further objects, features and advantages
of the invention will become apparent from the following
description of preferred embodiments with reference to the
accompanying drawings, wherein like numerals are used to represent
like elements and wherein:
[0023] FIGS. 1a and 1b are diagrams illustrating SOC variations in
a battery pack in accordance with the invention;
[0024] FIGS. 2a and 2b are diagrams illustrating SOC variations in
a battery pack in accordance with the invention;
[0025] FIG. 3 is a diagram illustrating the construction of a
charge/discharge control apparatus for the battery pack; and
[0026] FIG. 4 is a diagram illustrating SOC variations in a
related-art battery pack.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Preferred embodiments of the invention will be described
hereinafter with reference to the accompanying drawings. FIGS. 1a
and 1b are diagrams illustrating the variation in the
control-purpose SOC used by the HVECU 18 shown in FIG. 3. In both
cases of FIGS. 1a and 1b, the voltage of each cell 10 in the
battery pack 12 is detected by the voltage detector 14. From the
detected values, the battery ECU 16 computes the remaining
capacities of the individual cells 10. The battery ECU 16 then
determines a control-purpose SOC value, that is, a least SOC value
of the battery pack 12, from the least capacity value of the
computed remaining capacities. The control-purpose SOC value is the
least one of the SOC values of the cells 10, and is expressed as a
percentage of the least capacity value to the fully charged
capacity. Instead of the least SOC value, the least one of the
capacity values of the cells 10 determined by the battery ECU 16
may be used for the control.
[0028] On the basis of the control-purpose SOC value determined as
described above, the HVECU 18 performs the charge/discharge control
of the battery pack 12 so that the aforementioned SOC value is
within a predetermined range, for example, of 20% to 80%, by a
method as described above.
[0029] According to this control method, only the least SOC value,
among the SOC values of the cells 10 of the battery pack 12, is
used to perform the charge/discharge control. Therefore, the
process of computing the control-purpose SOC value can be
simplified.
[0030] As the time of use of the battery pack 12 increases, the SOC
values of the cells 10 vary to greater extents as indicated in FIG.
1b, and the greatest value of the varying SOC values becomes larger
than the greatest one of the SOC values exhibited immediately after
the initiation of use of the battery pack 12, that is, the greatest
one of the SOC values indicated in FIG. 1a. If in this case, the
charge/discharge control is performed using only the aforementioned
least SOC value, it is conceivable that the amount of charge of the
cell 10 with the greatest SOC value and/or a cell 10 having an SOC
value close to the greatest SOC value may increase beyond the
control range. However, as the SOC value of a cell 10 increases,
the charging efficiency of the cell 10 decreases and the
self-discharge thereof increases. Therefore, the increases in the
SOC values of the cells 10 at a greater SOC side in the range of
variation are curbed even though the charge/discharge control is
performed based on the least SOC value of the varying SOC values of
the cells 10. Hence, expansion of the variation in SOC beyond a
certain value will be avoided, without performing SOC
uniformalization by bringing each cell 10 to an overcharged state.
Thus, the need to perform the uniformalizing control is eliminated,
so that the service life reduction of the battery caused by
overcharge will be prevented.
[0031] Furthermore, the execution of the control using the least
SOC value, that is, the least one of the varying SOC values, will
prevent over-discharge of the cells 10 of the battery pack 12.
[0032] It should be noted herein that since the charge/discharge
control of the battery pack 12 is performed on the basis of the
least value of the varying SOC values, there is a possibility that
a cell 10 will be overcharged. Therefore, it is preferable that,
from the remaining capacities of the cells 10 of the battery pack
12, the greatest capacity value or the greatest SOC value be
computed, and that guard determination be made, that is,
determination be made as to whether a cell 10 is overcharged, on
the basis of the greatest capacity value or the greatest SOC value.
If any one of the cells 10 is overcharged, the upper limit value of
the control range of SOC of the battery pack 12 may be reduced by a
predetermined amount (e.g., about 10%) In this manner, overcharge
of the cells 10 can be substantially prevented.
[0033] The HVECU 18 also performs the charge/discharge control
through the use of the least one of the SOC values of all the cells
10 of the battery pack 12 if, from an initial state where all the
cells 10 are normal and merely exhibit a narrow range of SOC
variation as indicated in FIG. 2a, the SOC value of a cell 10 has
considerably dropped as indicated in FIG. 2b. As a result of this
manner of control, the state as indicated in FIG. 2b gradually
disappears, and recovery to a state close to the state indicated in
FIG. 1a can be achieved, due to the charging efficiency reduction
and the self-discharge increase of high-SOC cells 10 as mentioned
above.
[0034] As is apparent from the foregoing description, the invention
allows easy computation of a control-purpose SOC value since the
charge/discharge control of the battery pack 12 is performed on the
basis of the least value of the SOC values of the cells 10 of the
battery pack 12. Furthermore, since increase of the SOC values of
high-SOC cells 10 can be curbed, variations in SOC can also be
curbed.
[0035] Still further, if overcharge determination based on the
greatest SOC value of the varying SOC values finds that an
overcharged cell 10 exists, the upper limit value of the control
range of SOC of the battery pack 12 is changed to a reduced value.
Therefore, overcharge of the cells 10 can be substantially
prevented.
[0036] Although in the foregoing embodiment, the battery pack 12 is
controlled on the basis of the SOC or capacity value of the cells
10, it is also possible to control the battery pack on the basis of
the SOC or capacity value of each battery block since the battery
pack 12 has an arrangement in which a plurality of battery blocks
each having a plurality of serially connected cells 10 are serially
connected.
[0037] While the invention has been described with reference to
what are presently considered to be preferred embodiments thereof,
it is to be understood that the invention is not limited to the
disclosed embodiments or constructions. On the contrary, the
invention is intended to cover various modifications and equivalent
arrangements. In addition, while the various elements of the
disclosed invention are shown in various combinations and
configurations, which are exemplary, other combinations and
configurations, including more, less or only a single embodiment,
are also within the spirit and scope of the invention.
* * * * *